21216649 has 4 divisors (see below), whose sum is σ = 22139136. Its totient is φ = 20294164.

The previous prime is 21216631. The next prime is 21216659. The reversal of 21216649 is 94661212.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21216649 - 2⁹ = 21216137 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21216649.

It is not an unprimeable number, because it can be changed into a prime (21216619) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 461209 + ... + 461254.

It is an arithmetic number, because the mean of its divisors is an integer number (5534784).

Almost surely, 2^21216649 is an apocalyptic number.

It is an amenable number.

21216649 is a deficient number, since it is larger than the sum of its proper divisors (922487).

21216649 is an equidigital number, since it uses as much as digits as its factorization.

21216649 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 922486.

The product of its digits is 5184, while the sum is 31.

The square root of 21216649 is about 4606.1533843327. The cubic root of 21216649 is about 276.8379325389.

It can be divided in two parts, 212 and 16649, that added together give a palindrome (16861).

The spelling of 21216649 in words is "twenty-one million, two hundred sixteen thousand, six hundred forty-nine".